In many packet-oriented communication networks, such as for example Local Area Networks or Wide Area Networks, quality of service is not guaranteed for communication between terminals of these communication networks if no additional measures are taken to ensure it. The level of service of a connection is frequently referred to as “Quality of Service” (QoS) and can include various transmission and connection resources such as the transmission bandwidth, the transmission speed, the transmission delay and/or a permitted error rate.
For contemporary communication systems that are frequently based on such packet-oriented communication networks, what are known as resource managers are provided to ensure a specified quality of service. These are each assigned to a communication network or a subnetwork and manage its relevant transmission resources. A resource manager enables prespecifiable transmission resources to be reserved for connections to be set up in each case. The resource manager only allows a connection if its resource requirement does not exceed the transmission resources available for the primary route of the connection. After successful reservation of transmission resources the resource manager monitors the permanent availability rate of the reserved transmission resources for a particular connection.
To be able to establish whether transmission resources requested for a connection are available on the primary route of this connection through the communication network the resource manager needs information about the topology of the communication network, i.e. about the networking structure of the network nodes and link lines and about their relevant transmission capacity. This type of topology information which specifies the topology of a communication network is frequently referred to as a topology image.
In practical operation of a communication network this topology can occasionally change. Such a topology change can for example be caused by an administrative configuration change or by a failure or a recovery of a network component. As a result can there can be a dynamic change of communication routes in the communication network on Layer 2 (e.g., through so-called spanning-tree procedures) and/or Layer 3 (e.g., by routing procedures such as RIP or OSPF) of the OSI reference model.
On of the problems with this type of topology change is that a reservation or assignment of transmission resources made in a resource manager is then no longer consistent with the changed topology of the communication network. This can lead to an overbooking of transmission resources and thereby to a deterioration in the Quality of Service (QoS) of existing real time connections and new connections to be established.